The African and Asian slaves of course had to speak the master's tongue. Naturally they conversed in illiterate, simplified broken pidgin Dutch. Thus
the language spoken in the kitchen among the servants and slaves: Kombuis-Hollands,
Kitchen Dutch as opposed to Hoog Hollands: High Dutch.
Two centuries later both classes spoke the same tongue, called by then Cape Dutch.

The settlers, who still (1802) thought of themselves as Dutch, were now to be British subjects in perpetuity. In truth, they were no longer Dutch. After so many generations of separation from Holland, their language had undergone a remarkable metamorphosis, and taken aboard all manner of new words and usages from the various influences that the settlers had encountered. The British decided that this language was a worthless patois, not worth preserving. 1

From the 1870s, Afrikaans emerged as a separate language in the service of a cultural identity: White Afrikaanerdom.

The fact was ignored that about half of the speakers of the language were the darker-skinned descendants of slaves and the bastard offspring of the slaves and slave keepers.

At this stage the organisations that promoted the language, such as the Genootschap van de Regte Afrikaners (GRA) "Society of the True Afrikaners" referred to themselves as Africans to assert their identity as different from the Dutch. The name stuck.

There came to be one correct way to speak Afrikaans, and the other kinds became inferior by definition. The role of dark-skinned people in the language's origins
was not widely taught. The term 'Cape Dutch' fell out of favour by the 1920s, and the term Kitchen Dutch was regarded as a slur.
Afrikaans was a real language, after all.

Linguistic purity in Afrikaans, a simplified and bastardised form of Dutch,
is a paradoxical thing. Afrikaans is a melting pot language, not an
ivory tower one, and it is not the property of one skin-colour group.
Koos Kombuis's use of language forcibly reminds us of this.

Around the year 2000, most of the world's minority languages are disappearing or diminishing in importance.
Almost all native Afrikaans speakers also speak English. English speakers,
in general, are not as good at Afrikaans.
English is everywhere: on the radio, on TV, in print. It is impossible
to escape its influence. The aspirational images and lifestyles of the rich, the western cultural propaganda are all sold in English.
Ironically, Koos uses slang and English-influenced Afrikaans
to lament that influence.

Sources:http://www.rnw.nl/society/afrikaners/html/afrikaans.html
http://www.ned.univie.ac.at/publicaties/taalgeschiedenis/en/afrikaans.htm
1) This is from a history of the English settlers of 1820 at
http://perso.wanadoo.fr/euroleader/wedderburn/settlers/hist.htm